Summary
No matter how you slice the performance pie, it is clear that to ensure that you have satisfied, repeat customers online, you have to design for speed, feedback, and flow. Offering a consistently fast-loading web site with unambiguous feedback can contribute to a compelling online experience.
Give your users a sense of perceived control by offering them challenges matched to their skills. Use a simple layout with minimal distractions, offer interesting well- chunked and delineated content, and make navigation and performance transparent. Happy users are loyal users who will keep coming back to purchase your products and use your services.
Online Resources
http://elab.vanderbilt.edu/Vanderbilt's eLab research center is devoted to studying the Internet, including flow.
http://www.hcibib.org/HCI Bibliography features a searchable database of human-computer interaction resources.
http://www.humanfactors.com/Human Factors International has an excellent free monthly newsletter on user interface design issues.